Plants produce an enormous number of compounds of medical interest, many of which cannot be (economically) produced by de novo chemical synthesis. Identification of enzymes in plant natural product biosynthesis is an important goal, but one often frustrated by the intransigence of many plant species toward traditional techniques of biochemstry and genetics. Development of new methods to access these genetic resources is therefore essential. This proposal details development of a general method for selecting translational riboswitches controlled by a biosynthetic target of interest. Among many potential applications, such riboswitches can be applied to the identification of plant biosynthetic genes by a functional complementation strategy in yeast. The proposal includes two specific aims. First, a strategy for in vitro selection of translational riboswitches will be validated by selection of artificial riboswitches regulated by cocaine. Second, the best of the resulting switches will be used to clone the gene encoding ecgonine methyl ester benzoyltransferase from Erythroxylon coca. This enzyme catalyzes the final step in cocaine synthesis, and its identification may allow new strategies for control of this illegal drug. [unreadable] [unreadable] [unreadable]